1. Field of Invention
The invention relates generally to the fields of video and data transmission. In one aspect, the invention relates to the use of a on-demand (e.g., VOD) infrastructure in cable networks for high speed data download to set-top boxes (STBs).
2. Description of Related Technology
The provision of “on-demand” (OD) services, such as e.g., video on-demand or VOD, is well known in the prior art. In a typical configuration, the VOD service makes available to its users a selection of multiple video programs that they can choose from and watch over a network connection with minimum setup delay. At a high level, a VOD system consists of one or more VOD servers that pass and/or store the relevant content; one or more network connections that are used for program selection and program delivery; and customer premises equipment (CPE) to receive, decode and present the video on a display unit. The content is typically distributed to the CPE over a Hybrid Fiber Coaxial (HFC) network.
Depending on the type of content made available and rate structure for viewing, a particular VOD service could be called “subscription video-on-demand (SVOD)” that gives customers on-demand access to the content for a flat monthly fee, “free video-on-demand (FVOD)” that gives customers free on-demand access to some content, “movies on-demand” where VOD content consists of movies only, and so forth. Many of these services, although referred to by names different than VOD, still share many of the same basic attributes including storage, network and decoder technologies.
Just as different varieties of VOD service offerings have evolved over time, several different network architectures have also evolved for deploying these services. These architectures range from fully centralized (e.g., VOD servers at a central location) to fully distributed (e.g., multiple copies of content distributed on VOD servers very close to customer premises), as well as various other network architectures there between. Since most cable television networks today consist of optical fiber towards the “core” of the network which are connected to coaxial cable networks towards the “edge”, VOD transmission network architectures also consist of a mixture of optical fiber and coaxial cable portions.
The CPE for VOD often consists of a digital cable set-top box (DSTB) that provides the functions of receiving cable signals by tuning to the appropriate RF channel, processing the received signal and outputting VOD signals for viewing on a display unit. Such a digital set-top box also typically hosts a VOD application that enables user interaction for navigation and selection of VOD menu.
While the architectural details of how video is transported in the core HFC network can be different for each VOD deployment, each generally will have a transition point where the video signals are modulated, upconverted to the appropriate RF channel and sent over the coaxial segment(s) of the network. Depending on the topology of the individual cable plant, this could be performed at a node, hub or a headend. The coaxial cable portion of the network is variously referred to as the “access network” or “edge network” or “last mile network.”
In U.S. cable systems for example, downstream RF channels used for transmission of television programs are 6 MHz wide, and occupy a 6 MHz spectral slot between 54 MHz and 860 MHz. Deployments of VOD services have to share this spectrum with already established analog and digital cable television services. For this reason, the exact RF channel used for VOD service may differ from plant to plant. However, within a given cable plant, all homes that are electrically connected to the same cable feed running through a neighborhood will receive the same downstream signal. For the purpose of managing VOD services, these homes are grouped into logical groups typically called Service Groups. Homes belonging to the same Service Group receive their VOD service on the same set of RF channels.
VOD service is typically offered over a given number (e.g., 4) of RF channels from the available spectrum in cable. Thus, a VOD Service Group consists of homes receiving VOD signals over the same 4 RF channels. Reasons for this grouping include (i) that it lends itself to a desirable “symmetry of two” design of products (e.g. Scientific Atlanta's MQAM), and (ii) a simple mapping from incoming Asynchronous Serial Interface (ASI) payload rate of 213 Mbps to four QAM payload rates.
In most cable networks, VOD programs are transmitted using MPEG (e.g., MPEG-2) audio/video compression. Since cable signals are transmitted using Quadrature Amplitude Modulation (QAM) scheme, available payload bitrate for typical modulation rates (QAM-256) used on HFC systems is roughly 38 Mbps. In many VOD deployments, a typical rate of 3.75 Mbps is used to send one video program at resolution and quality equivalent to NTSC broadcast signals. In digital television terminology, this is called Standard Definition (SD) television resolution. Therefore, use of MPEG-2 and QAM modulation enables carriage of 10 SD sessions on one RF channel (10×3.75=37.5 Mbps<38 Mbps). Since a typical Service Group consists of 4 RF channels, 40 simultaneous SD VOD sessions can be accommodated within a Service Group. These numbers work out very well for many deployment scenarios, such as the following example. A typical “service area” neighborhood served by a coaxial cable drop from the cable network consists of 2000 homes, of which about two-thirds are cable subscribers, of which about one-third are digital cable subscribers, of which about 10% peak simultaneous use is expected. Hence, the bandwidth required to meet VOD requirements is 2000×(⅔)×(⅓)×0.1=approximately 40 peak VOD sessions—the exact number supported by a 4 QAM service group.
Several specific frameworks exist in the prior art for provisioning on-demand (e.g., VOD) and similar services to network subscribers. Notably, in the cable network context, the Interactive Services Architecture (ISA) specification (see, e.g., ISA Versions 1.4 and 1.5) published by the Assignee hereof describes techniques and mechanisms for distributing and delivering movie titles for VOD services. The ISA specification defines functional roles and interfaces that enable the development of pluggable interactive services in a cable environment. The focus of the ISA is primarily on viewer services, which are defined as the set of functions provided by the cable operator to its customers.
While having significant utility, the current ISA specification does not provide a mechanism for the delivery of non-video data such as large binary files, gaming applications, etc., especially at higher speeds which are necessary to maintain the customer's level of satisfaction with the download service.
Demand for High Speed Data
In conventional cable networks (including those compliant with the aforementioned ISA specification), a limited amount of data connectivity is offered between the head-end servers and the CPE (e.g., DSTBs) along with the television programming. Current techniques for sending “user” or non-programming data are intended for low bandwidth applications. Carousel mechanisms, wherein portions of the data are repeated periodically, are commonly used to provide such data services.
Unfortunately, the carousel scheme does not scale well for high bandwidth applications (or applications that require real time data delivery) for a variety of reasons including, e.g., that the CPE rate of data receipt is limited, and if the portions of data are received at the CPE too rapidly, the CPE may miss processing them entirely. This is especially critical for data which cannot sustain even a low level of bit errors (such as application or executable files). This “speed” restriction, coupled with the carousel delivery paradigm itself (i.e., periodic recurrent availability of data), results in comparatively long download times since the CPE has to wait for the next time a data file or portion of interest is transmitted by the data carousel.
Similarly, such conventional approaches lack a scheme wherein the CPE can provide feedback to the sender of such data in order to adjust the delivery speed to match that of the CPE data processing rate (or at least selectively instigate a retransmission of missed data without waiting for the cycle time of the carousel).
These limitations significantly restrict the use of such prior art mechanisms in emerging applications such as video gaming, and in other interactive television applications where a higher rate of download and lower latency of response is required.
Cable modem networks offer high bit-rate connectivity between a headend server and user premises. While such a connectivity solution can provide the bandwidth required for interactive applications, it is typically limited to “PC-centric” environments. Similarly, bandwidth is shared among users of a DOCSIS system; high bit-rate data transfer by each user can impact or adversely affect the bandwidth utilization of other users.
Furthermore, the utilization of VOD bandwidth in content-based networks is known to be non-uniform over time. In a conventional cable network, the unused bandwidth of a VOD channel cannot be used for cable modem data transmission due to the frequency segregation of the services.
A number of other approaches to data delivery (whether downstream or upstream) within a cable network are taught under the prior art. For example, U.S. Pat. No. 5,535,206 to Bestler, et al. issued Jul. 9, 1996 entitled “Upstream data transmission system for cable television” discloses a cable television upstream data transmission system that provides a plurality of time slots synchronized to the downstream symbol clock for use by subscriber terminals in upstream data transmission. The width and number of time slots are controlled by a pair of downloadable values to accommodate dynamic changes of the cable system.
U.S. Pat. No. 5,835,125 to Bhagavath issued Nov. 10, 1998 and entitled “Self-healing configuration for delivering data services on a hybrid fiber-coaxial (HFC) network” discloses the delivery of data services to subscriber clients located in a first access area using a modulated RF carrier signal over an HFC cable network. During times of failure, at least one channel within the roll-off spectrum above the passband of the coaxial amplifiers in the network is used as a protection data channel to supply these data services to the affected subscriber clients via an alternate signal path through an adjoining second access area. The data channel within the passband is upconverted to the roll-off spectrum and transmitted through the adjoining second access area which is interconnected to the first access area through a plurality of protection units. Each protection unit interconnects a side leg within each access area.
U.S. Pat. No. 5,841,468 to Wright issued Nov. 24, 1998 entitled “System and method for routing data messages through a cable transmission system” discloses a system and method for isolating data messages received from subscribers in a CATV system. The system includes a spectrum parallel router which receives data messages in the return spectrum of a service line at a service site. A switch at the service site directs data messages to service lines coupled to the site which have destination addresses corresponding to one of the service lines. Data messages not having a destination address corresponding to one of the service lines are provided to a transmitter for transmission to the next higher level of the CATV network over a return cable. Each service site has its own return cable which may be coupled to a distribution hub or a headend.
U.S. Pat. No. 5,991,308 to Fuhrmann, et al. issued Nov. 23, 1999 entitled “Lower overhead method for data transmission using ATM and SCDMA over hybrid fiber coax cable plant” discloses a process for reducing the amount of overhead data in ATM cell headers prior to transmission both upstream and downstream on an HFC cable plant using SCDMA on at least the upstream path, without loss of either IP or Ethernet addressing information. Downstream ATM cells are optimized by stripping off all but 2 bytes to leave a 50 byte cell. Incoming IP packets have their IP addressing information used to look up Ethernet domain address information. An Ethernet header is appended to each IP packet as is RFC 1483 bytes to signal the start of the packet. The packet is parsed into 48 byte ATM cell payloads.
U.S. Pat. No. 6,137,793 to Gorman, et al. issued Oct. 24, 2000 entitled “Reverse path multiplexer for use in high speed data transmissions” discloses a two-way hybrid fiber-coax cable network offering high-speed broadband communications delivered via a cable modem service. Bi-directional transmissions of packets between the head-end controller (Cable Modem Terminal System) and cable modems (subscriber terminal units) is accomplished using a cable television Media Access Control (MAC) protocol. In Hybrid Fiber-Coax (HFC) networks, the invention provides a Reverse Path Multiplexing (RPM) function permitting the coupling of a large number of return path (plant) RF ports (return ports) to be coupled to a receiver card in the CMTS.
U.S. Pat. No. 6,560,203 to Beser, et al. issued May 6, 2003 entitled “Method for changing type-of-service in a data-over-cable system” discloses a method and system for changing type-of-service in a data-over-cable system. The method and system allow a cable modem or a cable modem termination system to dynamically override the statically assigned type-of-service supplied to the cable modem in a Dynamic Host Configuration Protocol (“DHCP”) initialization sequence. A selection input can request a second type-of-service that may or may not be supported by the cable modem on the cable modem termination system. If the requested second type-of-service with an associated second quality-of-service is permitted on the cable modem, the cable modem termination system dynamically changes the first type-of-service to the requested second type-of-service.
United States Patent Publication No. 20020046406 to Chelehmal, et al. published Apr. 18, 2002 entitled “On-demand data system” discloses a system for allowing on-demand delivery of data, such as MPEG-2 compressed video data, to a subscriber from a content server. The system utilizes a managed IP network that is coupled to the one or more content servers that allows the content servers to deliver data such as video, audio, and textual data with a guaranteed quality of service that is at least as good as broadcast quality service. The managed IP network is connected to a head end or other local cable service provider where video is delivered locally to subscribers. The IP transport data is translated to MPEG transport data, multiplexed onto an MPEG transport system, digitally modulated onto an RF carrier and up-converted to a specific frequency channel. The signal is then applied to the cable for delivery to the subscriber. Upstream signaling occurs through a set top box or computer that is connected to the cable and subsequently to a digital modulator/demodulator and ISP to a managed IP network. Low band signals can also be transmitted from the content servers back to the set top box or computer indicating confirmation of an order. Also, control signals such as stop, rewind, fast-forward, and slow can be transmitted back to the content server to control the transmission of data from the content server to the subscriber.
United States Patent Publication No. 20020059635 to Hoang published May 16, 2002 entitled “Digital data-on-demand broadcast cable modem termination system” discloses methods and systems (including a cable modem termination system (CMTS)) for enabling a data-on-demand (DOD) digital broadcast system to provide digital DOD services via a communications medium over one or more channels. The cable modem termination system comprises: a communications network interface for receiving at least one DOD service from the DOD digital broadcast system, wherein the DOD service is formatted as a stream of data blocks arranged in a schedule such that a first data block of the DOD service may be accessed at any selected time period; a unidirectional network interface for providing the stream of data blocks to a plurality of users, wherein the users may access the first data block at any time period and may access subsequent data blocks of the stream of data blocks thereby accessing the at least one DOD service.
United States Patent Publication No. 20030058887 to Dworkin, et al. published Mar. 27, 2003 entitled “Method and apparatus for interleaving DOCSIS data with an MPEG video stream” discloses a cable modem system and method for interleaving MPEG video data frames with DOCSIS data frames. A cable modem system in accordance with the invention includes a cable modem termination system (CMTS) that is adapted to detect the presence of null packets in an MPEG video data stream and insert DOCSIS data frames in there place. The source of the MPEG video data stream determines the clock rate at which the MPEG data stream is routed through the CMTS.
While the foregoing citations illustrate a broad variety of different prior art data transmission techniques, all such techniques generally suffer from one or more of the following disabilities: (i) requiring significant modifications or upgrades to existing cable system infrastructure and associated standards; (ii) not providing sufficiently high data download rates along with low service latency; and/or (iii) not providing mechanisms for control of the data stream via the CPE (including error correction, retransmission, and pause/restart capability).
Based on the foregoing discussion, it is evident that improved apparatus and methods are needed to provide high-speed data connectivity between two nodes on a content-based network, e.g., the cable system head-end and the CPE. Such apparatus methods would ideally be able to utilize available bandwidth from the OD (e.g., VOD) spectrum, and also use the existing OD infrastructure. It would further be advantageous if such data apparatus and methods could be added to a network without requiring significant modifications to system hardware (e.g., servers and CPE), which tends to impede the implementation of new services and increase the cost of such implementation.